I was working on the IR’s and came up with a couple of questions that i need help with!!! The first thing that i have to ask is that when i had a sensor working, the signal on dashboard viewer was not solid it would either flash on and off or it would just be solid off! I don’t think this should be happening so could you give me a hand.
The second thing is that I soldered one of these vishay sensors to a pwm cable and then the sensor imput was solid green no matter where the sensor was facing, covered or not.
How are other teams attaching thier sensors to the controller?? I tried a pwm cable that i took of the male end and I soldered the wire to the pins of the connector, and the problem I had was the imput always on (possibly from the heat!)
Can anyone tell me how they are attaching thier sensors and any other help on these sensors would be appreciated!!!
the signal should be flashing on and off - remember, these are pulse signals so that the two beacons can be distinguishable. you’ll need to use code that like on www.kevin.org/frc to record the pulses and translate them into an actual input of whether or not the beacon is seen.
when you soldered the sensor to the wires, did you cross the wires over like it shows in the sensor drawings? if you plug them straight into a pwm cable, the wrong signals will be on the pins
if your sensor is on solid then something is wrong, you should get a pulse with a 10mS period if its seeing the beacon - BTW the beacon is very bright and bouces off walls in small rooms, people, boxes… and covering it with your hand wont block the light. you really need to be out in a large open space to work with the IR system.
It sounds like you burned the sensor. You need to be very careful with heat around them. Always use a heat sink (an alligator clip works fine) between the soldering and the sensor, and use a low wattage soldering iron.
See photo gallery Dale(engr] 2004 robots 2-17,
IR hooded receivers top/bottom (in sockets)
Use of PWM cable requires the Red & Black pins reversed prior to soldering.
For test purposes
construct a special male to male PWM cable
and plug-in the receivers in to test.
I use a PWM “Y” insert
with the 2nd male end flared for observation with the scope probe & gnd.
(a current limited +5v power supply may be substituted for the DIG IN side
power (red/black) set to ~.05A, receivers need ~5mA .005A
for bullet proof protection while testing)
The Vishay 34840 & 4840 receivers do not respond to continuous (DC) IR.
The IR Beacon must pulse at 40kHz ±~2kHz, (50-50 duty cycle).
The receiver very selectively accepts only 40 kHz on=off pulsed IR,
rejecting less than ~38kHz or greater than ~42kHz or continuous IR (DC)
Correct Pulses are provided by the EDU controller with Beacon code running.
The best way to observe proper Receiver operation is with an oscilloscope.
see photo gallery Dale(engr] 2004 Beacon scope waveforms
Probe the 4840 Output pin:
with no pulsed IR present, voltage level is a constant +5vDC,
when 40 kHz is detected, level is 0v (ground) for 1 ms or 2 ms
“this is called active LOW” and what we look for in the code
then back high for the remainder of the period - 9mS or 8 ms,
The cycle repeates every 10mS (100Hz)
The scope is also a good way to view fidelity of the IR signal.
Reflections/weakness often show up as shorter irratic and/or dropout pulses.
Observe care to avoid:
Output pin to +5v shorts when 40kHz IR is active
as this may damage them (we have 3 dead)
(see previous post: the output voltage never goes below ~2.5v
In this fault there is a negative going pulse upon detection, but it’s
truncated, i.e. stops short of 0V.
The DIG INP requires the voltage level to go
less than ~.5V [TBD] to signal IR pulses detected.)
Note that a DMM does not give a clear 0V reading in the presence of pulsed IR
due to the short duty cycle, the average is close to +5v (= no IR state)
but a small but discernable decrease from 5v can be seen.
(even with a strong signal the output Voltage is high (+5V)
90% (2ms) to 95% (1ms) of the cycle)